The invention relates to the consequences of the occurrence of ventricular extrasystoles (VES) on the operation of these implantable devices.
A VES is generally defined as a spontaneous depolarization of the ventricle that was not preceded, in a given interval of time, by an associated spontaneous atrial event (i.e., natural depolarization of the atrium) or stimulated atrial event (i.e., a pulse of low energy delivered by the device to the atrium to cause a depolarization of the atrium). The interval in question is typically an interval defined by a temporal window selected in a range from between 31 and 300 ms preceding the detection of the ventricular activity.
One can also consider that there is a VES when the device detects a ventricular activity that is preceded by an atrial event in an interval of time included in the aforementioned window (e.g., between 31 ms and 300 ms), but with an atrio-ventricular delay (AVD) of the examined cardiac cycle that is less than a given duration (for example, less than 31 ms) to the AVD of the preceding cardiac cycle. The cardiac cycle is defined as the interval of time between two events of a comparable nature in the same cavity.
For further details on the extrasystoles, one will be able to refer to the published EP-A-0 550 342 and its corresponding U.S. Pat. No. 5,312,451, commonly assigned herewith to ELA Médical, which describes an algorithm for the detection and treatment of VES. U.S. Pat. No. 5,312,451 is incorporated herein by reference in its entirety.
In practice, patients present at the basal state a certain number of isolated VES without adverse consequences. But when these extrasystoles become too frequent, the phenomenon can deteriorate the filling of the cavities, and thus the hemodynamic function of the heart. Frequent VES also can facilitate the appearance of disorders of the cardiac rhythm, which may or may not be related to a degradation of hemodynamic performance.
The current pacemakers typically have an associated control algorithm that on detection of a VES will consider that it relates to a cardiac cycle and re-trigger the counting of the various delays, in particular a ventricular escape interval (VEI) that is recycled (i e., starts over). This is done to avoid triggering a ventricular fibrillation by delivering an inappropriate stimulation. But these known devices always react in a systematic and undifferentiated way when they detect a VES.
The starting point of the invention lies in the observations by the inventor that the effects of the VES can be variable, from one patient to another, and also for the same patient from one VES to the next, and that it can be convenient to differentiate how the device responds to a VES according to the foreseeable effects of the detected VES. Indeed, the spontaneous ventricular activity resulting from a given VES can have very variable physiological effects: from the absence of any effect to the blocking of a complete cardiac cycle, with the most frequent intermediate situation being a notable fall in the ejected blood volume, because of a contraction that is of poor quality or out of phase as compared to the remainder of the cardiac cycle.
Thus, for example, when a VES occurs at the end of the systolic phase, i.e., when the myocardium is indeed contracted, the VES will temporarily block this contraction (more specifically, the uncontraction). As a result, there will be no further influx (inflow) of blood into the organ throughout this blocking. For another example, if the VES occurs at a moment when the myocardium is not contracted or only a little contracted, it will cause a mechanical contraction of the cavity involving the expulsion of a blood volume.
One will understand that, to optimize the hemodynamic function of the patient, the next ventricular stimulation will have to intervene at a different moment, according to the situation. This can be obtained, for example, by a suitable adaptation of the VEI used by the pacemaker to define the next moment for stimulation. The VEI is defined as the interval of time, counted after a detection or a stimulation in the ventricle, following which a stimulation is delivered to this same ventricle if no spontaneous event is detected.